A study of the signal transduction mechanisms governing the complex interactions between steroid hormones and growth factors leading to the proliferation of breast cancer cells would lead to a clearer understanding of the processes mediating tumor growth and metastasis. The interaction of growth factors such as epidermal growth factor (EGF) and insulin-like growth factors (IGF-1) and IGFII with their receptors on breast cancer cells can trigger a cascade of events including the hydrolysis of phospholipids to lipids such as arachidonic and linoleic acids. The hypothesis to be tested in this project is whether these fatty acids or their metabolites play a key role in estrogen and growth factor-induced growth of breast cancer cells. In order to test our hypothesis we propose to examine the basal, estrogen, EGF- and IGF-induced activation of these pathways by studying protein and RNA expression of specific enzymes which produce oxidative metabolites of arachidonic acid and linoleic acid in breast cancer cell lines and tissues. We will also test the functional significance of these pathways by, 1) using molecular biologic and pharmacologic approaches to block these pathways and, 2) Directly study the effects of the oxidized products of arachidonic and linoleic acid on estrogen and growth factor induced proliferation of the breast cancer cells. Cell-cycle changes and cyclin D1 expression in the presence of these oxidized products of arachidonic and linoleic acid. The effects will be compared to those seen in a normal control breast cell, MCF-10F, and in normal tissue samples. As potential mechanisms we will examine, a) the role of activation and overexpression of specific protein kinase C isoforms in the cancer cells and tissue of tyrosine kinase; b) whether these products alter the activity and expression of the aromatase enzyme which leads to local estrogen synthesis; c) whether these products can modulate IGF-I receptor expression. Our completed studies should lead to the revelation of new mechanisms of the process of tumor formation and progression as well as novel therapeutic options for the treatment or prevention of breast cancer.